Flame retardant treated fabrics with low formaldehyde content

ABSTRACT

The instant invention relates to a textile article comprising a flame-retardant treated fabric including an oxidized polymer obtained from an ammonia curing of a condensate of (i) a tetrakis (hydroxyorgano) phosphonium salt; and (ii) urea or thiourea; followed by an oxidation into phosphine oxide groups of at least one part of the phosphonium groups present on the cured condensate, wherein said flame-retardant treated fabric: —is intended to be used as a stable substrate in which the formation of formaldehyde over the time is inhibited; and —contains less than 1% by weight of phosphorus present in phosphonium groups, based on the total weight of the flame-retardant treated fabric.

The instant invention relates to textile articles comprising (or consisting in) a fabric treated by flame-retardant polymer obtained from an ammonia curing of a condensate of (i) a tetrakis (hydroxyorgano) phosphonium salt (also referred as “THP⁺ salt”); and (ii) urea and/or thiourea (herein referred as “(thio)urea”); followed by an oxidation into phosphine oxide groups of at least one part of the phosphonium groups present on the cured condensate.

Flame retardant treatments of this type are well known and has been described e.g. in the European patent application EP 0 709 518. In these treatment, the fabric to be treated is generally impregnated with the condensate of the THP⁺ salt and (thio)urea (optionally together with an amine as described in EP 0 709 518, such as an aliphatic amine having 12 carbon atoms or more, such as n-dodecylamine; n-octadecylamine, n-hexadecylamine, and/or n-eicosylamine) and, typically, the fabric is then dried and then cured with ammonia (NH₃) whereby a phosphonium-based polymer is produced within the fibers of the fabric, which is mechanically fixed to the fabric. After the curing, the obtained polymer is oxidized in order to convert at least a part of the trivalent phosphorus (carried by the phosphonium group) into a pentavalent phosphorous (an phosphine oxide group). Examples of fabrics treated according to this process and textile articles and garments made thereof are those sold under the trademark PROBAN®.

In the scope of the instant invention, the inventors have now found that a fabric treated according to the above-mentioned process tends to generate formaldehyde over the time. Concretely, in many cases, the free HCOH content increase with the time and, generally, becomes greater than 100 ppm or even greater than 300 ppm over a few years. The term “free HCOH content” as used in the instant description refers to the content of free formaldehyde (HCOH) in the fabric as measured according to the European standard No. EN ISO 14184-1.

This identified formation of formaldehyde constitutes a potential bar, because of the toxicity of formaldehyde. Especially, a fabric intended to be in contact with the human skin should have a very low content of HCOH, typically of less than 300 ppm, more preferably less than 200 ppm for an indirect contact (with another piece of clothes between the fabric and the skin) and of less than 100 ppm, preferably less than 75 ppm.

The instant invention aims at providing a flame retardant treatment process making use of the materials which lead to a low content of formaldehyde that remains low over the time.

To this end, the instant invention proposes to make use of the above mentioned process but in specific conditions, that have been found inhibit the formaldehyde formation over the time. Namely, the inventors have now surprisingly found that a limitation of the content of trivalent phosphorus (i.e. phosphorus of phosphonium groups by opposition of pentavalent phosphorus of the phosphine oxide groups >P═O) in the treated fabric leads to a strong decrease of the formation of formaldehyde.

Especially, the inventors have now shown that when a fabric has a content of trivalent phosphorous, i.e. of the phosphorus present in phosphonium groups, of less than 1% by weight based on the total weight of the flame-retardant treated fabric, then substantially no formaldehyde HCOH is generated over the time. The inhibition of the formation of HCOH is even more efficient when the content of trivalent phosphorous is lower than 0.9%, and even more when lower than 0.8%.

On this basis, according to a first aspect, one subject matter of the instant invention is a textile article, such as an item of clothing for example, comprising at least one flame-retardant treated fabric including an oxidized polymer obtained from an ammonia curing of a condensate of (i) a tetrakis (hydroxyorgano) phosphonium salt; and (ii)urea and/or thiourea; followed by an oxidation into phosphine oxide groups of at least one part of the phosphonium groups present on the cured condensate,

wherein said flame-retardant treated fabric:

-   -   is intended to be used as a stable substrate in which the         formation of formaldehyde over the time is inhibited, for         example for a long term contact with the skin; and     -   contains less than 1% by weight, preferably less than 0.9% by         weight and even more preferably less than 0.8% by weight of         phosphorus present in phosphonium groups (trivalent phosphorus),         based on the total weight of the flame-retardant treated fabric.

In a textile article according to the invention, the molar ratio P3:P5 of the trivalent phosphorus (as present in the phosphonium groups) to the pentavalent phosphorus (as present in the phosphine amide groups) is typically of less than 60%, for example of about 50%. The total content of phosphorus in a fabric according to the invention is typically of around 2% based on the total weight of the flame-retardant treated fabric.

Another subject matter of the instant invention is a process for preparing the above mentioned textile article, comprising:

-   -   (a) a flame retardant treatment of the fabric, including:         -   (a1) an impregnation of said fabric with the condensate             of (i) a tetrakis (hydroxyorgano) phosphonium salt; and (ii)             urea or thiourea         -   (a2) a curing with ammonia of the impregnated condensate;         -   (a3) an oxidation of the polymer resulting from the curing,             typically with H₂O₂     -   (b) an analysis of the content of the phosphonium groups in the         fabric, followed by a repetition of the sequence of the steps         (a3) and (b) if the analysis shows that the fabric contains 1%         or more of phosphorus present in phosphonium groups, based on         the total weight of the flame-retardant treated fabric.

Step (a3) may be followed by a washing of the oxidized fabric obtained in step (a3), typically by immersion within at least one (for example 2 or 3) washing bath, typically a water-containing washing bath.

In the process of the invention, step (b) comprises an analysis wherein the content of trivalent phosphorus is checked and adapted if needed. The analysis may for example be made by ³¹P NMR, that allows to distinguish a phosphonium peak at around 25 ppm and an amine oxide peak at around 47 ppm

If needed, the sequence of the steps (a3) and (b) are repeated many times until the sought trivalent phosphonium content is not below the sought value.

According to a specific embodiment, the sequence of the steps (a3) and (b) may be repeated even after having obtained a content below the sought value (for example if a very low content of trivalent phosphonium is sought.

According to a possible embodiment, in step (b), the analysis is followed by a repetition of the sequence of steps (a3) and (b) if the analysis shows that the oxidized polymer contains 0.9% or more of phosphorus present in phosphonium groups, based on the total weight of the flame-retardant treated fabric

According to yet another aspect, the invention relates to the use of a flame-retardant treated fabric containing less than 1% by weight, preferably less than 0.9% by weight and even more preferably less than 0.8% by weight of phosphorus present in phosphonium groups (trivalent phosphorus), based on the total weight of the flame-retardant treated fabric, as a substrate stabilized against formation of formaldehyde, for example for a long term contact with the skin.

The expression “long term” contact with the skin, especially include a contact with the skin, preferably more than one year, more preferably more than 2 years, and even more preferably at least 3 years, after the synthesis of the oxidized polymer.

In the scope of the instant invention, the inventors have now shown that, in some specific conditions, step (a) systematically allows to obtain the sought content of trivalent phosphorous, i.e. of the phosphorus present in phosphonium groups, of less than 1% of phosphorus present in phosphonium groups, based on the total weight of the flame-retardant treated fabric. More precisely, it has now been found that, surprisingly, when the oxidation step (a3) is carried out in the presence of a metabisulfite salt used a pH of less than 4 (typically when the oxidation using H₂O₂ is followed by a treatment using a metabisulfite salt at a pH of less than 4, contrary to the usual conditions wherein metabisulfite salt is used as a scavenger but at a pH of at least 5, typically of at least 6), then the step (a) systematically leads to a trivalent phosphorous content of less than 1% (with sodium metabisulfite at a pH of about 2, this content is of about 0.8%). Therefore, when step (a) is conducted in these specific conditions, there is no need of step (b).

Accordingly, another specific subject matter of the instant invention is a process that directly allows to obtain a flame-retardant treated fabric according to the present invention, that contains less than 1% by weight, generally less than 0.9% by weight and in most cases less than 0.8% by weight of phosphorus present in phosphonium groups (trivalent phosphorus), based on the total weight of the flame-retardant treated fabric. This specific process, that do not need the implementation of a “checking” step (b) as defined above, contains a flame retardant treatment, including the following steps:

-   -   step 1: an impregnation of said fabric with the condensate         of (i) a tetrakis (hydroxyorgano) phosphonium salt; and (ii)         urea or thiourea, preferably followed by a drying     -   step 2: a curing with ammonia of the impregnated condensate;     -   step 3: an oxidation of the polymer resulting from the curing,         typically with H₂O₂, said oxidation including and/or being         followed by a treatment with a metabisulfite salt, preferably         sodium metabisulfite, at a pH of below 4, preferably below 3,         for example at a pH of 1.5 to 2.5, (e.g. from 1.8 to 2.2,         typically of about 2).

Typically, in step 3, an oxidation is first carried out using hydrogen peroxide H₂O₂ or another oxidant, and then the treated fabric is treated with a metabisulfite salt, preferably sodium metabisulfite, at a pH of below 4, preferably 3, for example at a pH of 1.5 to 2.5, typically with SMBS at a pH of about 2.

Different features and specific embodiments of the invention are described in more details herein-after:

According to a first variant, the textile article of the invention is intended to be in indirect contact with the skin (namely with a layer of clothing between the treated surface and the skin). In that case, it is advantageous that it comprises less than 300 ppm, preferably less than 200 ppm of free formaldehyde, as measured according to the European standard No. EN ISO 14184-1.

According to a second variant, the textile article of the invention is a intended for direct contact with the skin. Then, it is highly preferable that it comprises less than 75 ppm of free formaldehyde, as measured according to the European standard No. EN ISO 14184-1.

According to a specific embodiment, the tetrakis (hydroxyorgano) phosphonium salt is tetrakis (hydroxyorgano) phosphonium chloride (THPC). Alternatively, it may be advantageous that the tetrakis (hydroxyorgano) phosphonium salt is tetrakis (hydroxyorgano) phosphonium sulfate (THPS)

The treated fabric advantageously comprises cellulosic fibers, for example natural cellulosic fibers such as fibers of cotton, linen, jute, or hessian; or regenerated cellulosic material.

According to a specific embodiment, the treated fabric essentially comprises (typically for at least 95%) cellulosic fibers.

According to another embodiment, the fabric may comprise a mixture of cellulosic fibers together with non cellulosic fibers, said non cellulosic fibers being for example natural fibers such as wool or silk, or synthetic fibers such as polyester, polyamide, or aramid. As an example, the fabric may comprise a mixture of 60% cotton and 40% polyester.

The invention will now be further illustrated by the following illustrative example.

EXAMPLE 1

Two treated fabrics having a total content of phosphorus of 2% based on the total weight of the flame-retardant treated fabric have been compared:

-   -   Fabric 1: Comparative     -   containing trivalent phosphorus at a content more than 1% of         based on the total weight of the flame-retardant treated fabric     -   Fabric 2: according to the invention     -   containing trivalent phosphorus at a content of 0.9% of based on         the total weight of the flame-retardant treated fabric

The free HCOH content on the fabric has been measured and are reported in the table below:

Free HCOH content (pppm) time Fabric 1 Fabric 2 (years) (comparative) invention) 0 100 100 0.5 125 100 1 150 100 2 205 100 3 305 100

EXAMPLE 2

In order to illustrate the advantages of the succession of step 1 to step 3 of the process of the invention, a comparison test has been conducted on fabric treated with PERFORM chemical, ammonia cured and oxidised with hydrogen peroxide according to the standard industry procedure, using sodium metabisulfite (SMBS) at a pH of 5, and the same but using sodium metabisulfite (SMBS) at a pH of 2

More precisely, a fabric treatment has been carried out as follows:

-   -   Impregnation     -   514 g of a fabric was immersed in a bath having the following         composition: 481 g of PERFORM CC (available at Solvay) in 519 g         of water as a solvent.     -   The fabric was then immediately passed through a pad mangle and         into an oven for drying at 120° C. for approximately 1 minute.     -   Ammonia curing     -   The PERFORM CC treated fabric was then subjected to an ammonia         atmosphere for 15 seconds by passing through an ammonia cure         unit.     -   After sampling this resulted in 577 g of impregnated and cured         fabric.     -   H₂O₂ Oxidation     -   The 577 g of cured fabric was then immersed for 10 minutes in a         bath with the following composition: 2 L of 35% hydrogen         peroxide in 8 L of water as a solvent.     -   The fabric was then immersed for 15 minutes in another bath with         the following composition: 100 g of soda ash in 10 L of water as         a solvent.     -   The fabric was then immersed for 45 minutes in another bath with         the following composition: 10 L of water.     -   The fabric was then immersed for 5 minutes in another bath with         the following composition: 10 L of water, whereby a bulk         oxidised fabric (BOF) is obtained.     -   Sodium metabisulfite treatment     -   As a comparative test, a first sample (Sample 1) of the BOF as         obtained after the treatment steps as defined above was treated         at a pH of 5.     -   As an illustration of the instant invention, the same treatment         has been carried out on a second Sample of the BOF (Sample 2),         in exactly the same conditions as for Sample 1, but with a         treatment at a pH of 2.         -   Sample 1 (Comparative test)             -   13.4 g of the BOF (=Sample 1) was immersed in a bath                 with the following composition: 27.4 g of 40% sodium                 metabisulfite in 1 L of water as a solvent, with a                 resulting pH of 5, for 5 minutes at 70° C.             -   Sample 1 was then immersed for 5 minutes in another bath                 with the following composition: 1 L of water at 80° C.             -   Sample 1 was then immersed for 5 minutes in another bath                 with the following composition: 1 L of water at 80° C.             -   Sample 1 was then immersed for 5 minutes in a bath with                 the following composition: 1 L of water at 20° C.         -   Sample 2 (Illustrative)             -   13.9 g of the BOF (=Sample 2) was immersed in a bath                 with the following composition: 27.4 g of 40% sodium                 metabisulfite plus 40 g of 1M HCl in 1 L of water as a                 solvent, with a resulting pH of 2 for 5 minutes at −70°                 C.             -   Sample 2 was then immersed for 5 minutes in another bath                 with the following composition: 1 L of water at −80° C.             -   Sample 2 was then immersed for 5 minutes in another bath                 with the following composition: 1 L of water at −80° C.             -   Sample 2 was then immersed for 5 minutes in another bath                 with the following composition: 1 L of water at 20° C.

As a result, a trivalent phosphorus content of less than 1% (0.84%) has been obtained when SMBS is used at pH=2 according to the invention (Sample 2).

On the other hand, a content of more than 1% (1.26%) has been obtained in the standard conditions using SMBS is used (sample 1)

With the content of less than 1% as obtained according to the invention, the free content of HCOH remains very low and stable over the time (Sample 2), when it increases with the time with the standard conditions of treatment (sample 1). 

1. A textile article comprising at least one flame-retardant treated fabric including an oxidized polymer obtained from an ammonia curing of a condensate of (i) a tetrakis (hydroxyorgano) phosphonium salt; and (ii) urea and/or thiourea; followed by an oxidation into phosphine oxide groups of at least one part of the phosphonium groups present on the cured condensate, wherein said flame-retardant treated fabric: is intended to be used as a stable substrate in which the formation of formaldehyde over the time is inhibited; and contains less than 1% by weight of phosphorus present in phosphonium groups, based on the total weight of the flame-retardant treated fabric.
 2. The textile article according to claim 1 wherein the flame-retardant treated fabric contains less than 0.9% by weight of phosphorus present in phosphonium groups, based on the total weight of the flame-retardant treated fabric.
 3. The textile article according to claim 1 intended to be in indirect contact with the skin, with a clothing between the treated surface and the skin, that comprises less than 300 ppm.
 4. The textile article according to claim 1 intended to be in direct contact with the skin, that comprises less than 75 ppm of free formaldehyde.
 5. The textile article according to claim 1, wherein the tetrakis (hydroxyorgano) phosphonium salt is tetrakis (hydroxyorgano) phosphonium chloride (THPC).
 6. The textile article according to claim 1, wherein the tetrakis (hydroxyorgano) phosphonium salt is tetrakis (hydroxyorgano) phosphonium sulfate (THPS).
 7. The textile article according to claim 1, wherein the oxidized polymer is obtained from an ammonia curing of a condensate of (i) a tetrakis (hydroxyorgano) phosphonium salt; (ii) urea and/or thiourea, together with an aliphatic amine having 12 carbon atoms or more; followed by an oxidation into phosphine oxide groups of at least one part of the phosphonium groups present on the cured condensate.
 8. A process for preparing a textile article as defined in claim 1, the process comprising: (a) a flame retardant treatment of the fabric, including: (a1) an impregnation of said fabric with the condensate of (i) a tetrakis (hydroxyorgano) phosphonium salt; and (ii) urea or thiourea, optionally together with an aliphatic amine having 12 carbon atoms or more, (a2) a curing with ammonia of the impregnated condensate; (a3) an oxidation of the polymer resulting from the curing, (b) an analysis of the content of the phosphonium groups in the fabric, followed by a repetition of the sequence of the steps (a3) and (b) if the analysis shows that the fabric contains 1% or more of phosphorus present in phosphonium groups, based on the total weight of the flame-retardant treated fabric.
 9. The process of claim 8, wherein in step (b), the analysis is followed by a repetition of the sequence of steps (a3) and (b) if the analysis shows that the oxidized polymer contains 0.9% or more of phosphorus present in phosphonium groups, based on the total weight of the flame-retardant treated fabric.
 10. A process for preparing a textile article as defined in claim 1, the process comprising the following steps: step 1: an impregnation of said fabric with the condensate of (i) a tetrakis (hydroxyorgano) phosphonium salt; and (ii) urea or thiourea; step 2: a curing with ammonia of the impregnated condensate; step 3: an oxidation of the polymer resulting from the curing, said oxidation including and/or being followed by a treatment with a metabisulfite salt at a pH of below
 4. 11. A method, comprising using a flame-retardant treated fabric including an oxidized polymer obtained from an ammonia curing of a condensate of (i) a tetrakis (hydroxyorgano) phosphonium salt; and (ii) urea and/or thiourea; followed by an oxidation into phosphine oxide groups of at least one part of the phosphonium groups present on the cured condensate, wherein said flame-retardant treated fabric contains less than 1% by weight of phosphorus present in phosphonium groups, based on the total weight of the flame-retardant treated fabric, as a substrate stabilized against formation of formaldehyde.
 12. The method according to claim 11, wherein the flame-retardant treated fabric is used for a long term contact with the skin.
 13. The method according to claim 12, wherein the long term contact with the skin is for more than one year after the synthesis of the oxidized polymer.
 14. The method according to claim 13, wherein the long term contact with the skin is for more than two years after the synthesis of the oxidized polymer.
 15. The method according to claim 14, wherein the long term contact with the skin is for more than three years after the synthesis of the oxidized polymer.
 16. The textile article according to claim 3, comprising less than 200 ppm of free formaldehyde.
 17. The process according to claim 8, wherein, in (a3), the oxidation of the polymer resulting from the curing is with H₂O₂.
 18. The process according to claim 8, wherein, in (b), the analysis of the content of the phosphonium groups in the fabric is by ³¹P NMR.
 19. The process according to claim 10, wherein, in step 3, the treatment with a metabisulfite salt is at a pH below
 3. 